Papermakers felts and method of making them



United States Patent 3,093,880 PAPERMAKERS FELl'S AND METHOD OF MAKINGTHEM William J. McLaughlin, Rensselaer, N.Y., assignor to HnyckCorporation, New York, N.Y., a corporation of New York No Drawing. FiledFeb. 29, 1960, Ser. No. 11,415

9 Claims. (Cl. 28-722) This invention relates to papermakers felts. Moreparticularly it relates to the felts which are used at the wet end ofpapermaking and similar machines of the various types used in theproduction of felted fibrous products such as paper, paperboard,box-board, pulp laps and asbestos-cement boards, shingles and pipes. Ingeneral these so-called wet felts" are used to pick up and to transporta freshly formed fibrous web through various dewatering devices in whichthe moisture content of the web is reduced to such a point that the webbecomes self-supporting.

Papermakers wet felts should be as stable and durable as possible andalso must have the characteristics of porosity and surface finishappropriate for the particular fibrous product being produced. The mostwidely used felts have been woven from woolen yarns and they have beenfulled to form a stable and durable structure. Pulling is conducted in afulling mill in which the fabric is worked in hot water, with or withoutadditives, to promote felting of the fibers. Such operation requires asubstantial period of time and results in some reduction in one or bothdimensions of the fabric with attendant firming of the woven fabric, allas well known in the art. Stability and durability are enhanced by theuse of larger diameter yarns and by weaving them closely together. Onthe other hand, porosity is enhanced by the use of small diameter yarnswoven loosely. One or both of the surfaces of the woven structure may betreated as by brushing, teaseling, and the like, to form a nap,particularly when critical grades of paper or other products are to bemade wherein surface markings corresponding with the woven pattern ofthe felt would be objectionable. Napping of woven fabric by brushing orteaseling is a subtractive process in that the fibers that are raised toform the nap are necessarily removed from the body of the yarns withresultant reduction in strength and in many cases a reduction indurability as regards abrasion resistance. To secure better finishcharacteristics with relatively open weave fabrics it is necessary toraise a substantial number of fibers to bridge the nap over therelatively large interstices between the yarn crossings.

Thus, it will be apparent that in the design and construction of wovenwet felts, compromises must be made between what may be desired in theway of durability, porosity, and finish, because emphasis upon any oneof these characteristics may be achieved only at the expense of one orboth of the others. The effect is to limit the ranges of each of thesecharacteristics which may be combined in a practical and satisfactoryproduct.

It is an object of the present invention to provide wet felts whichembody those features which have made the traditional woven and fulledwet felts desirable and in addition, provide for compatible achievementof greater durability, more desirable porosity and unusually finefinishing characteristics in much broader ranges of combination thanheretofore available.

Broadly speaking, the objectives of this invention are achieved byproviding a woven base fabric capable of substantial fulling, to whichis needled on one or both sides, unwoven fibrous material which willenhance the stability of the fabric and which may be applied in suchquantity as to provide any nap that may be required for desiredfinishing characteristics, abrasion resistance and the like. Afterneedling, the felt is fulled to final dimensions by traditionaltreatment in a fulling mill. The fulling provides a firm and durablestructure and locks the needled fibers firmly in the fabric. The fullingalso smooths the mapped surface or surfaces by reducing or obliteratingthe pattern of needle holes.

A simplified flow diagram of a process in accordance with one preferredembodiment of the invention is as Since stability and durability of thefelt are enhanced by the needled fibers the base fabric may be more openin weave and thus have greater porosity while still having desiredstability and durability. Furthermore, the application of needled fibersto form nap is additive rather than subtractive insofar as strength isconcerned whereby the imparting of finish characteristics is not made atthe expense of strength.

A particularly important feature of the present invention is that thefullable base fabric is a good cushion and needs only a thin layer ofunwoven fiber to cover the yarns. Such a thin layer could not beexpected to cover and till in the openings between the yarns toestablish a smooth surface of uniform porosity. However, because thefabric is fulled after needling, the fibers in the applied layer whichextend over and into the openings of the base fabric are condensedwithin each opening inasmuch as the openings are reduced in size byfulling. The yarns do not decrease in diameter during fulling but ratherbecome firmer, and the filling yarns, especially, tend to increase indiameter. Thus the inner surface of the applied layer of fiber isconformed to the undulations of the base fabric while the other surfaceremains substantially planar.

The finished felts produced in accordance with this invention thus maypresent a smooth and uniform napped surface on one or both sides whensuch a surface or surfaces may be desired for imparting fine finish topaper or other fibrous webs. The smoothness and uniformity of thesurface can be made to exceed that of conventional woven and nappedfelts wherein the concentration of fibers raised by teaseling isgreatest at the yarns and is smallest in the openings between yarns.Consequently, it has been necessary to raise a teaseled nap that may betoo heavy at the yarns and still may be insufficient in the openings. Incontrast with this, the present invention atfords concentration ofneedled fibers in the openings whereby the added fibers produce a smoothsurface with an unexpectedly uniform porosity in all areas of thefinished felt. Because of this uniformity the quantity of added fibermay be kept at a minimum to favor good porosity while still achieving afine finish.

The felts of the present invention are an even greater improvement overthe needled felts heretofore available comprising coarse base fabrics ofnon-fullable fiber, such as cotton, to which unwoven fleeces of naturalor synthetic fibers or blends of natural and synthetic fibers areneedled to one or both sides. While, in the past, structures of thistype have found some utility in connection with the manufacture offibrous webs wherein finish is not important, they have not found much.success in the :production of fine papers or other products requiringgood finish. With these structures, wherein the base fabric is a hard,open, sleazy construction more similar to fishnet than to a papermakersfelt, it has been necessary to apply, by needling, very substantialquantities of non-woven fibrous material merely to cover the coarse yarnstructure and to stabilize the open sleazy weave. Even greaterquantities are needed if it is attempted to bridge the openings in theweave. When such large quantities of added fiber are used the porosityof the resultant structure is non-uniform and usually isunsatisfactorily low at the beginning and rapidly decreases as a resultof plugging in use.

In an attempt to improve the characteristics of the needled feltsavailable in the past, it has been proposed to utilize fleeces ofsynthetic fibers or blends of natural and synthetic fibers which willnot tend to full during use of the felt. The synthetic fibers thusproposed have surfaces which are smoother than the surfaces of woolfibers and are less likely to retain solid materials. However, the basefabric, which is usually cotton, does not have a sufficient tendency toretain the needled fibrous material and particularly to retain needledsynthetic fibers, in firmly anchored condition. As a result,considerable difiiculty has been experienced in shedding of fibersduring use, which fibers may adhere to the paper to such an extent as todowngrade the paper.

Also, it has been proposed in the past to use as a base fabric one whichhas been woven from natural fibers such as wool and which has beenfulled prior to needling. Here again it has been considered essentialthat all tendency of the base fabric to full be utilized before theneedling so that the final product will exhibit no tendency towardfulling when it is put into use. While the resultant structure somewhatmore closely resembles a papermakers felt because it has a woolen basefabric, the needled nap cannot afford uniform porosity and smoothsurface unless it is applied in layers of such thickness that theoriginal porosity is too low for most practical applications. It will beapparent that the thick layers are required whenever it is attempted toprovide a smooth outer surface because the applied nap must havesufiicient strength and stability in itself to bridge the openingsbetween the yarns of the base fabric. Thus the provision of good finishcharacteristics is approximately as incom patible with high porosity andfreedom from plugging when a fulled base fabric is used as it is when anonfullable base fabric is used. The tendency toward shedding of fibersis also present when a fulled base fabric is used and increasing thenumber of needle penetrations per unit area in an effort to more firmlyentangle the fibers tends to reduce the strength of the yarns in thebase fabric.

The design and construction of papermakers felts in accordance with thepresent invention represents an approach to the problem which differsfundamentally from the approach represented by needled felts heretoforeused or proposed. In one sense the present invention represents theutilization of base fabrics which themselves are conventional Wovenpapermakers felts consisting of fullable fibrous yarn structures and theformation on said structures of a nap or naps by needling of additionalfiber rather than by teaseling fibers from the yarn structure. Becausethe structure is fulled after needling the needle holes through theyarns are closed. The added fibers are firmly gripped by the yarns ofthe base fabric and they are distorted out of the generally linear orperpendicular path followed by the fibers during insertion there-of intothe yarns by the needles and the needling loom. Each yarn of the finalstructure thus is interlocked with the added fiber by randomentanglement. The porosity of the final felt is not dependent upon theexistence of the needle holes with vertically directed fibers therein asare the needled felts heretofore proposed.

The strength, durability and drainage characteristics of felts made inaccordance with this invention may be established by the selection, oververy wide ranges, of yarns, yarn counts and weaves for the base fabricwith the knowledge that desired finish characteristics and uniform,stable porosity may be derived from the fibers which are added byneedling. Because unexpectedly good finishing characteristics may beobtained by the needling to such a base fabric of thin, continuous battsof unwoven fiber, the woven base fabric may be made of substantiallycoarser, stronger yarns woven more openly than could have been used inthe manufacture of a conventional felt with a raised nap.

In some instances the fullable base fabric chosen for a particular feltin accordance with this invention may be originally woven in such anopen pattern as to be sleazy and subject to deformation and damage ifhandled. In such cases the base fabric should be partially fulled beforeneedling to make it sufiiciently firm to withstand handling but stillcapable of substantial additional falling. in other instances the basefabric may be sufiiciently firm as originally woven so that all fullingmay be performed after needling.

The base fabric, as woven, or partially fulled as desired, is thenplaced in the needling loom and the desired quantity of non-woven fiberis needled to one or both sides in the usual fashion. The unwoven fiberpreferably is in the form of smoothly carded batts or fleeces which areof sufficient width and length to form a uniform layer throughout thearea of the side of the base fabric to which they are to be applied.

The needling loom preferably is arranged to produce a random pattern ofclosely spaced needle penetrations through the layer of unwoven fiberwhereby the barbs on the needles will carry individual fibers or smallgroups thereof downwardly into the yarns and openings of the basefabric. The fibers engaged by the needle barbs thus become intimatelyentangled with the yarn structure of the base fabric as well as withother fibers in the unwoven fleece. A substantial portion of the lengthof most of the unwoven fibers, however, will remain in generallyhorizontal position so that when needling is completed the entire areaof the base fabric will be covered by a quite firm, smooth andhorizontally disposed nap.

After the nap has been applied to one side of the base fabric it may befulled and otherwise treated and finished for use. However, it may bedesired to turn the fabric in the needle loom to needle the oppositeside. In some instances a similar or different type of unwoven fiber maybe needled to the opposite side and in other instances the opposite sidemay be needled without additional fiber to turn certain of the fibers ofthe first layer back upon themselves, thus to become more firmlyentangled with and secured to the base fabric. When layers are to beadded to both sides it is sometimes preferred to perform an additionalneedling with bare needles on the side opposite that to which the lastlayer was applied.

The woven base fabrics for use in the present invention may be made fromyarns at least a substantial percentage of which are fullable and theymay be woven endless or they may be woven in continuous lengths the endsof which are joined by splicing to form endless structures. When wovenendless the weft yarns extend lengthwise of the endless belt of fabricand when woven as continuous lengths the warp yarns extend lengthwise ofthe spliced belt of fabric. In either event at least a substantialpercentage of the yarns should be fullable for use in the presentinvention. The fullable yarns may consist entirely of natural fiberssuch as wool or they may consist of blends of natural fibers withsuitable synthetic fibers such as polyamide, polyester,polyacrylonitrile, polyparaffin, polyvinyl and polyvinylidene fibers andsimilar fibers including fibers made of copolymers of any suchmaterials. The blended yarns must contain sufilcient quantities ofnatural fiber to be capable of substantial fulling.

The non-woven fiber may be fullable or not as desired. When fullablefibers or fullable blends of fibers are used the needled nap will fullalong with the base fabric, the most noticeable effect being a reductionin thickness with increase in firmness of the nap. In addition, thefullable nap will tend to full to the base fabric thus enhancing thefirmness of attachment of the nap to the base fabric. When non-fullablefibers or blends are needled to the fullable base fabric the averagethickness of the nap is little affected by fulling of the final felt.However, in both instances the applied non-woven fibers will condense toa substantially greater degree within the interstices of the weave thanthey will over the yarns. This condensation of fibers within theinterstices of the weave can be so controlled by selection of quantityof applied fiber and selection of the yarns, yarn count and weave of thebase fabric as to provide in the fulled final product a porosity withinthe interstices which is substantially the same as the porosity of theinherently porous, cushiony yarns of the base fabric.

In view of the fact that paperrnalters wet felts in their intended usedo not behave like sieves but rather must have porosity in at least twodirections the uniformity of porosity which may be achieved throughoutthe body of felts made in accordance with this invention is ofparticular value. It is vastly preferable to the non-uniform, sieve likeconstructions heretofore produced by needling fibers to bases which aredeliberately incapable of fulling in order that the needle perforationsand vertically positioned fibers may promote drainage only in onedirection.

It has been indicated above that finish characteristics suitable for themanufacture of fine paper can be achieved in accordance with thisinvention by the use of thinner layers or batts of unwoven fibers thathave been used in the past. Direct comparison is not practicable sincethe thinnest layers heretofore needled to cotton or other nonfullablebase fabrics have only been effective to cover the yarns and tostabilize the sleazy base fabric and the weave pattern of the basefabric is inevitably marked on the paper or other product. For example,with non-fullable base fabrics with relatively coarse yarns and openweave it has not been possible to use less than about 2-02. per squarefoot (finished dimensions) of non-woven fibers simply to obtain thestabilization and yarn cover mentioned above. In contrast with this thepresent invention makes it possible to produce a true papermakers wetfelt with excellent finish characteristics when about 1 /2 oz. or lessper square foot (finished dimensions) of unwoven fiber is needled to afullable base fabric of similarly coarse open construction which isthereafter fulled to its finished dimensions. With other constructionsof fullable base fabrics much less added fiber may be needed to giveexcellent finishing characteristics. Finishing char acteristics to meetvarious demands may be obtained by the use of progressively lighterapplied naps, all the way down to the lower limit established by theability to form continuous non-woven webs of fiber, which, in thepresent state of the art is believed to be about 5 oz. per square foot(of the web).

The reason that the present invention permits of so little non-wovenfiber to meet varying finish requirements is that the stability andbonding of the woven base fabric comes primarily from fulling and is notsolely dependent upon the needled fiber as in the case of non-fullablebase fabrics. The full range of quantity of added non-woven fiber isthus available for the design of felts in accordance 6 with thisinvention to produce felts ranging from extremely light weight feltswith coarse finish or fine finish to extremely heavy, dense felts withmany heavy layers of added fiber. This invention is also applicable tofullable base fabrics woven with two or more plies of fabric of the sameor of different construction, yarn count or other characteristics. Forexample, a relatively fine count and small yarn diameter may be used foran upper ply while a coarser, stronger construction may be used for theback ply. In such event, the finish characteristics of the upper ply maybe still further improved by the needling thereto of a very moderateamount of unwoven fiber, followed by fulling of the whole structure.

No unusual fulling techniques are necessary in connection with feltsmade in accordance with the present invention. Well known procedureswith respect to time, temperature, amount of manipulation and the likemay be followed in the same manner as heretofore applied to themanufacture of fullable, woven felts. In those cases under the presentinvention wherein the base fabric is partially fulled before needling itis preferred that such partial fulling not exceed about of the totalfullability of the fabric and in many cases a substantially largeramount of fullability may be left for fulling after the needlingoperation.

In some situations, such as in cases where extremely fine finishcharacteristics are of particular importance, it is advantageous to trimthe added non-woven fibers forming the nap to a substantially uniformlevel in any well known manner. As an illustration, the nap may betrimmed by shearing or singeing, for example, to thereby further insurea smooth and even surface finish.

As indicated heretofore, upon the completion of the final fulling of thefabric, the added non-woven fibers are firmly anchored to the basematerial. As a result, the tendency toward shedding of fibers during useis substantially reduced, and the possibility of the paper beingdowngraded as a result of such shedding is diminished. Particularly forextremely fine grades of paper, it is sometimes desirable to apply avacuum to the fabric to remove any extraneous unanchored fibers andthereby further reduce the possibility of shedding. Such vacuumingpreferably is accomplished after the final fulling, although the fabricmay be in either its wet or dry state or both. Thus, in one particularlyadvantageous arrangement, the fulled fabric is first vacuumed in its wetcondition and is then dried and trimmed. The vacuuming of the fabric inits Wet state not only serves to loosen any extraneous fibers but alsoorients the nap forming fibers in an upright position, thereby greatlyfacilitating trimming. Upon the completion of the drying and trimmingoperations, the fabric is again vacuumed to remove any remainingunanchored fibers, including those separated from the nap duringtrimming.

:In other cases, such as where the deleterious effects of shedding areof minor importance, the vacuuming and/ or trimming operations safelymay be eliminated without departing from the spirit or scope of theinvention.

The terms and expressions which have been employed are used as terms ofdescription and not of limitation, and there is no intention in the useof such terms and expressions, of excluding any equivalents of thedescribed features, or portions thereof, it being recognized thatvarious modifications are possible within the scope of the inven tionclaimed.

What is claimed is:

l. The method of making a papermakers felt comprising a woven basefabric with a nap of non-woven fibrous material firmly secured to atleast one side thereof, which consists of weaving a base fabric fromyarns at least some of which contain suificient fullable fiber materialto render the woven fabric capable of substantial fulling, needling acontinuous batt of non-woven fibrous material to at least one side ofsaid fullable woven base fabric, and fulling said fullable base fabricwith said fibrous material 7 rfieledled thereto to form a fulled nappedpapermakers 2. A papermakers felt made in accordance with the processset forth in claim 1.

3. The method of making a papermakers wet felt comprising a woven basefabric with a nap of non-woven fibrous material firmly secured to atleast one side thereof, which consists of weaving a base fabric fromyarns at least some of which contain sufficient fullable fibrousmaterial to render said woven base fabric capable of substantialfulling, needling a continuous batt of fullable non-woven fibrousmaterial to at least one side of said fullable woven base fabric, andthereafter simultaneously fulling said fullable woven base fabric andthe non-woven fibrous material needled thereto, to thereby form a fullednapped papermakers felt with non-woven fibers firmly interlocked withand fulled to the yarns of said base fabric.

4. The method of making a papermakers wet felt comprising a woven basefabric with a nap of non-Woven fibrous material firmly secured to atleast one side thereof, which consists of weaving a base fabric fromyarns at least some of which contain sufficient fullable fibrousmaterial to render said woven base fabric capable of substantialfulling, needling a thin, continuous batt of non-woven fibrous materialto at least one side of said fullable woven base fabric, and fullingsaid fullable woven base fabric with the non-woven fibrous materialneedled thereto, to thereby form a fulled napped papermakers felt withnonwoven fibers firmly interlocked with the yarns of said base fabricand condensed to a greater degree within the interstices of said fabricthan over said yarns, the amount of non-woven fibrous material needledto said base fabric being not greater than about one and one-half ouncesper square foot of the fulled base fabric.

5. The method of making a papermakers wet felt com prising a woven basefabric with a nap of non-woven fibrous material firmly secured to atleast one side thereof, which consists of weaving a base fabric fromyarns at least some of which contain sufficient fullable fibrousmaterial to render said woven base fabric capable of substantialfulling, preliminarily partially fulling said base fabric to a pointwherein it is still capable of substantial further fulling, needling acontinuous batt of non-woven fibrous material to at least one side ofsaid partially-fulled woven base fabric, and thereafter completing thefulling of said woven base fabric with said fibrous material needledthereto to form a fulled napped papermakers felt.

6. A papermakers felt made in accordance with the process set forth inclaim 5.

7. The method of making a papermakers wet felt comprising a woven basefabric with a nap of non-woven fibrous material firmly secured to atleast one side thereof, which consists of weaving a base fabric fromyarns at least some of which contain sufficient fullable fibrousmaterial to render said woven base fabric capable of substantialfulling, preliminarily partially fulling said base fabric to a point notin excess of about eight-five percent of the total fullability of saidfabric, needling a continuous batt of non-woven fibrous materialcontaining fullable fibers to at least one side of said partially-fulledwoven base fabric, and thereafter simultaneously completing the fullringof said woven base fabric and fulling the non-woven fibrous materialneedled thereto, to thereby form a fulled napped papermakers felt withnon-woven fibers firmly interlocked with and fulled to the yarns of saidbase fabric.

8. The method of making a papermakers wet felt comprising a woven basefabric with a nap of non-woven fibrous material firmly secured to atleast one side thereof, which consists of weaving a base fabric fromyarns at least some of which contain sufficient fullable fibrousmaterial to render said woven base fabric cap-able of substantialfulling, preliminarily partially fulling said base fabric to a pointwherein it is still capable of substantial further fulling, needling athin, continuous batt of nonwoven fibrous material to at least one sideof said partially-fulled woven base fabric, and thereafter completingthe fulling of said woven base fabric with the non-woven fibrousmaterial firmly secured to at least one side therepapermakers felt, theamount of non-woven fibrous material needled to said base fabric beingnot greater than about one and one-half ounces per square foot of thefulled base fabric.

9. The method of making a papermakers wet felt comprising a woven basefabric with a nap of non-woven fibrous material needled thereto to forma fulled napped of, which consists of weaving a base fabric from yarnsat least some of which contain sufficient fullable fibrous material torender said woven base fabric capable of substantial fulling, needling acontinuous batt of non-woven fibrous material to at least one side ofsaid fullable woven base fabric, fulling said fullable woven base fabricwith the non-woven fibrous material needled thereto, to thereby form afulled napped papermakers felt with non-woven fibers firmly interlockedwith the yarns of said base fabric and condensed to a greater degreewithin the interstices of said fabric than over said yarns, andvacuuming said fulled napped papenmakers felt in its wet condition.

References Cited in the file of this patent UNITED STATES PATENTS Re.21,890 Walsh et al Aug. 26, 1941 84,235 Waring Nov. 24, 1868 667,699Heaton Feb. 12, 1901 1,002,177 Reynolds Aug. 29, 1911 2,588,228 GatesMar. 4, 1952 2,930,106 Wrotnowski et al Mar. 29, 1960 FOREIGN PATENTS556,186 Great Britain Sept. 23, 1943

1. THE METHOD OF MAKING A PAPERMAKERS FELT COMPRISING A WOVEN BASEFABRIC WITH A NAP OF NON-WOVEN FIBROUS MATERIAL FIRMLY SECURED TO ATLEAST ONE SIDE THEREOF, WHICH CONSISTS OF WEAVING A BASE FABRIC FROMYARNS AT LEAST SOME OF WHICH CONTAIN SUFFICIENT FULLABLE FIBER MATERIALTO RENDER THE WOVEN FABRIC CAPABLE OF SUBSTANTIAL FULLING, NEEDLING ACONTINUOUS BATT OF NON-WOVEN FIBROUS MATERIAL TO AT LEAST ONE SIDE OFSAID FULLABLE WOVEN BASE FABRIC, AND FULLING SAID FULLABLE BASE FABRICWITH SAID FIBROUS MATERIAL NEEDLED THERETO TO FORM A FULLED NAPPEDPAPERMAKERS FELT.